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Highest quality through automation

Сase studies

Sabine Koll, K-ZEITUNG

Smaller batches, more complex molds, and increasingly demanding quality requirements – those are the reasons why Kroma International, with main office in Lahr, Germany, has started a project to increase efficiency in its injection molding operation. One component of that effort is the installation of linear robots on all injection molding machines over 1,000 kN clamping force. For WITTMANN BATTENFELD, the delivery to Kroma was their 7,000th W818 robot. Sales Manager Andreas Hollweg and Sales Engineer Manfred Nerz, who has been handling customer support for Kroma for a long time now, set out together to personally hand over the CNC robot – along with a commemorative certificate – to Kroma’s General Manager Erik Männle.

While WITTMANN BATTENFELD already has decades of experience with robot systems, this type of equipment application is still relatively new to Kroma. Until recently, the owner-managed company had equipped only their large injection molding machines with handling systems in order to be able to remove large and heavy components – and those were supplied together with the machine.


Kroma General Manager Männle praises the WITTMANN robot systems’ easy programming and operation.
(Photo: K-ZEITUNG)

Linear robots for greater efficiency
In 2015, an order for six linear robots to be retrofitted to existing machines in the medium clamping force range was placed with WITTMANN BATTENFELD, including the W818. Kroma now wants to invest further in automation: “Having focused the efficiency increase project in moldmaking in 2014, we expanded it last year to the injection molding area. Equipping the injection molding machines with robots plays a key role in that context”, says General Manager Männle.
Männle took over the company in 2002 and has been expanding it continuously ever since. Today he employs some 90 people in design, in mold-making, and in the injection molding area. Kroma generated sales of EUR 9.2 million in 2014. For 2015, Männle expects to break the EUR 10 million mark. The lion’s share of sales is generated in the injection molding segment, and 20% comes from the mold sector.

Forty-two molds are made every year with 18 metalworking machines. In all, Kroma has nearly 800 molds in its production department today. Kroma has more than 38 machines with clamping forces ranging from 200 kN to 7,750 kN, most of which were supplied by WITTMANN BATTENFELD. Those machines produce parts weighing from 0.1 g to 2 kg, and three of them are designed for two-component applications. Insert molding of components is also one of the production techniques Kroma provides to its customers. Those customers come from an extremely broad spectrum of sectors, ranging from the automotive industry and household appliances to construction and medical technology. “On the one hand, that variety is a big advantage, because we are not dependent on any one industry. That definitely helped us a lot during the 2008/2009 crisis”, explains Männle. “On the other hand, that heterogeneity creates significant challenges for us in injection molding production. Moreover, we have only a few products running continuously on the machines, the batch sizes are getting smaller and smaller in many sectors, and that means we have to change molds often. But we still have to be able to manufacture cost-effectively and deliver rapidly, because many customers are reducing their inventories and want to have the parts delivered on demand instead.” So he is obliged to use standardized machines, automation and processes.

More broadly, in order to outperform competitors from Eastern Europe and elsewhere over the long term, Kroma is striking a balance between cost-effective production on the one hand and specialty products on the other. Examples of their specialty products include technical parts made from hardto-process, high-temperature resistant plastics such as PPS, PPSU and PEEK. Männle is convinced: “The only way for an injection molding operation to survive in Germany is by concentrating on specialty products and/or offering logistical advantages. This can take the form of suitable storage services or, where the size of the components makes it uneconomical for the customer, to transport them over long distances.” The air ducts produced by Kroma in high volumes on their large injection molding machines represent but one example of this.

Along with its own mold-making operations, Männle sees an additional advantage in his company having its own engineering department. This enables Kroma to offer complete projects to its customers – from development to moldmaking to production, all from a single source. “As a result, we are able to acquire new customers through engineering while also offering very fast response to customer demands.”

Although Kroma has been growing for years now, Männle also feels the price pressure on the market. That’s why he imposed measures to increase efficiency in the injection molding area in 2015, together with the goal of achieving increased quality. “The two are closely interconnected”, insists Männle. “When we supply goods and then the customer later complains and rejects them, that costs us money and hurts our image. We want to improve that performance significantly.”

Equipping nearly all of the injection molding machines in the medium clamping force range with robots is a fundamental part of this quality and efficiency drive. “With robots, the process runs with far greater consistency and precision”, explains Männle. “The employees in the production department operate multiple machines. Sometimes they were unable to clear all of the parts from the conveyor belts fast enough to prevent stoppages. As a result, the injection molding machines had to be shut down.” When material remains in the nozzles, that has a negative impact on part quality. Kroma’s removal robots now ensure that cycle times are precisely maintained.

Another benefit is that the robots now automatically place parts from family molds (right-left variants, for example) in separate packages, thereby eliminating the need for manual sorting and the potential for mix-ups. This speeds up assembly and improves quality.

The handling systems from the WITTMANN Group have ultimately reduced the part reject rate where falling had previously been a potential source of deformation. Overall processes have also been streamlined through the placement of parts directly into their packaging.

Retrofit in-progress
Kroma now wants to gradually retrofit all medium-size injection molding machines with robots, as well as certain smaller machines in special cases. The use of a robot, for example, eliminated the need for a sophisticated unscrewing system on a 400-kN injection molding machine which Kroma uses to make fine screws out of PPSGF. Männle is convinced that the decision to continue in the direction of consistent automation was the right one: “We are improving quality in production and reducing costs. And the robots from WITTMANN BATTENFELD are very user-friendly and easy to program, so we have very few handling problems.”

As far as Kroma’s General Manager is concerned, the quality and efficiency drive in their injection molding operation is not over yet. He now plans to introduce a PD (production data acquisition) and CAQ (computer-aided quality assurance) system, so that the settings and parameters required for the individual parts can be transmitted to the machines from a central point and the actual data can subsequently be played back for quality assurance purposes. “This will enable us to optimize the specification data, thereby closing the control loop. In this way I hope not only to reduce the error rate even further, but also to raise overall efficiency through shorter downtimes.”

Long term, Männle also wants to implement organizational changes. “There is hardly a machine technician anywhere who knows all of the functionalities of modern injection molding machines. More and more manual skills are now being replaced by modern technology. Consequently, the role of machine technicians will tend to involve more process support, monitoring and optimization in the future. In that context, we will need production supervisors to monitor the machines via the PDA system. Manual intervention in the machine control system will then become the exception and not the rule.”

Sabine Koll is a trade journalist. This article first appeared in the March 11, 2016 issue of K-ZEITUNG.

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